On June 16, 2001, about 1130 eastern daylight time, a DeHavilland DH-82 Tiger Moth, N4797, registered in the experimental category, was substantially damaged during collision with trees and terrain after takeoff from Weiss Farm Airport (JY24), Allamuchy, New Jersey. The certificated commercial pilot/owner and passenger were not injured. Visual meteorological conditions prevailed for the personal flight that originated at the pilot/owner's strip destined for The Old Rhinebeck Airport (NY94), Rhinebeck, New York. No flight plan was filed for the flight conducted under 14 CFR Part 91. The pilot provided a statement to a Federal Aviation Administration (FAA) aviation safety inspector. According to the inspector's record of interview: "[The pilot] stated that the field is 2,300 feet long and was on a 055 Runway heading with a 5-knot wind. He performed an engine mag check preflight, and found it to be okay. He had full power and headed down the runway. He was airborne about halfway down the runway, and then the engine felt like it was not performing, as if it did not have enough power to get over the trees, and he settled the aircraft into the trees about 1,000 feet from the end of the runway. The aircraft had full fuel. It was filled about two weeks earlier." During a telephone interview, the pilot said the purpose of the flight was to fly to the Old Rhinebeck Airport for a fly-in and show. He said the weather was "terrible" first thing in the morning, but cleared around 1100. The pilot said he performed a preflight inspection, engine start, run-up, and magneto check with no anomalies noted. He said he taxied the airplane to the approach end of the 2,300-foot grass strip for a departure to the east. According to the pilot: "The engine sounded terrific. I looked for the wind, but there wasn't much - 7 to 8 knots - right down the runway. I held the brakes, added full power, and then started to go. I lifted the tail as soon as I could because there are high trees at the end, no doubt about it. "I passed the windsock about halfway down, and we were climbing, but then all of a sudden we just started losing power. I looked ahead and there was no opening. The plane was mushy, and we just mushed into the trees. When I realized we weren't going to make it, I throttled back." The pilot was asked if he perceived a loss of engine RPM on the tachometer. He said: "No. I checked the airspeed only. I didn't look at any other instrument." The pilot/owner said the engine continued to run as the airplane descended through the trees and struck terrain. During a telephone interview, the passenger said: "The weather was murky. We called ahead to see how the weather was at Orange County and Rhinebeck. Around 1115, the weather was improving so we decided to go up and have a look. The winds were about 5 or 6 knots down the runway. "The preflight seemed fine. We did the run-up and everything seemed 'tickety-boo.' We ran it up for 4 to 5 minutes, up to full power; the mags were fine, ran it up and took off. "As we got to about 100 feet, it just sort of didn't produce full power. It didn't stop; it just reduced. It seemed to be a loss of engine rpm. There was a definite change in note to the engine. I've got about 200-odd hours in the Moth, and it just seemed to be an engine thing, not an angle-of-climb thing." The passenger said he did not remember seeing a drop in engine rpm on the tachometer. He said the engine was operating at 2,100 rpm during the takeoff. The passenger said the maximum allowable rpm was 2,300 and that the cruise power setting was 1,950 rpm. He also said the throttle was full forward throughout the takeoff and initial climb. When asked if he had any concerns about a takeoff from a 2,300-foot grass strip with tall trees at the departure end, he passenger replied: "That's plenty of room, I promise you." The pilot's son witnessed the accident from the runway. He said: "I was standing on the runway and it looked like a perfect takeoff, but it never seemed to gain altitude. He got out above the trees, turned it into the wind, disappeared over the trees, and then I heard the crash." "The engine sounded sweet. It sounded good. It never missed a beat. I watched him run it up. He checked the mags and it sounded good, sounded sweet." "I watched that plane takeoff hundreds of times and it didn't sound any different." The pilot stated the airplane was full of fuel, and with two passengers, remained well below the maximum allowable gross weight. The pilot held a commercial pilot certificate with a rating for airplane single engine land. He held a private pilot certificate with a glider rating. The pilot's most recent medical certificate was issued September 9, 1998, and was valid for 15 months from the date of the examination. The pilot reported 3,450 hours of flight experience, 590 hours of which were in the Tiger Moth. The pilot stated the airplane was full of fuel, and with two passengers, remained well below the maximum allowable gross weight. The passenger held a foreign-based private pilot certificate with a rating for airplane single engine land. His most recent third class medical certificate was issued June 27, 2001. The weather at Morristown, New Jersey, 20 miles southeast of the pilot's strip, was a broken ceiling at 1,500 feet with 3 miles of visibility in mist. The temperature was 80 degrees and the dewpoint was 73 degrees. The pressure altitude was about 1,500 feet. Interpolation of takeoff performance charts revealed that from a 2300-foot runway of short, dry grass, at 1,500 feet pressure altitude, the airplane was capable of a takeoff over a 50-foot obstacle at its maximum gross weight of 1,825 pounds. A certificated airframe and powerplant mechanic examined the engine and shared his findings with an FAA aviation safety inspector. According to the inspector, the examination revealed that the engine could be rotated by hand, but that the exhaust valve in the #1 cylinder remained fixed in the open position. The crankshaft was rotated through several more times before the valve was freed, and subsequently opened and closed completely.